1. Field of the Invention
The present invention relates to an image forming apparatus employing electrophotography or electrostatic recording and, more specifically, relates to an image forming apparatus, such as a copy machine, a printer, or a facsimile machine.
2. Description of the Related Art
Conventional vertical-path type image forming apparatuses having an image-forming unit disposed in a paper-conveying path (hereinafter referred to as ‘vertical path’) for conveying a sheet of paper from a lower side to an upper side of the image forming apparatus and then ejecting the sheet of paper from the image forming apparatus are discussed in Japanese Patent Laid-Open Nos. 09-297440 and 2004-151568.
Such image forming apparatuses, as illustrated in prior art FIG. 8, were realized as a result of digitalization. Digitalization has enabled a document image reader 1 that is a scanner for reading a document and an image-forming unit 2 that is a unit for carrying out an image-forming process in the image forming apparatus to be optically separated in the image-forming unit 2.
In such an image forming apparatus, optical information read out by the document image reader 1 is converted into an electronic signal at a photoelectric conversion unit, such as a charge-coupled device (CCD), and is sent to the image-forming unit 2. The electric signal is converted into an optical signal at a predetermined unit. In this way, image information is transmitted to a photosensitive drum 11 and a latent image is formed on the photosensitive drum 11.
Since the emission position of the optical signal may be any predetermined position, the flexibility of the position for the writing on the photosensitive drum 11 is increased. To correspond to this increased flexibility, a laser beam 12 has been used as a writing unit.
A vertical path type image-forming process has become possible to be employed in image forming apparatuses because of the technical development in draw-up systems and downward cleaning systems. A draw-up system is provided to supply toner upwards from image-forming units, such as a development unit 13 and a toner supplying unit 14, to the photosensitive drum 11 disposed above the image-forming units and to supply toner upwards from a developer or toner storage container to a development sleeve 17 disposed at a position higher than the developer or toner storage container. A downward cleaning system is provided to reliably clean the photosensitive drum 11 using a cleaning unit having an opening on the bottom that is contacts the photosensitive drum 11 for cleaning.
Since it has become possible to employ the vertical path system in an image forming apparatus, the image forming apparatus can employ a short-path structure wherein a paper conveying unit 18 and a fixing unit 19 are disposed above the image-forming units and an ejecting unit 5 and an ejecting slot 21 are disposed above the paper conveying unit 18 and the fixing unit 19. Image-forming units, including a paper-feeding unit 3 having a paper cassette, a registration unit 4, the photosensitive drum 11, the development unit 13, and the cleaning unit, are disposed in this order from the bottom in the image forming apparatus. According to this structure, the conveying path from the paper-feeding unit 3 to an ejecting unit 5 can be formed without extreme curving. In this way, the conveying path becomes short and the number of components included in the conveying path can be reduced.
Furthermore, since the conveying path passes through the image forming apparatus relatively linearly, the space required for the conveying path is reduced. In this way, the size and cost of the image forming apparatus is reduced and the amount of time required for a sheet of paper to pass through the conveying path is reduced. Since the flexibility of the layout of each component in the image forming apparatus increases, the components can be disposed in a highly dense manner. As a result, the space required for disposing the components is reduced, and thus the size of the image forming apparatus is reduced.
However, the vertical path passing through a photosensitive drum unit 20 and the fixing unit 19 cannot be shortened in a conventional image forming apparatus since rails 22-a and 22-b configured to guide the photosensitive drum unit 20 during mounting or dismounting are disposed on the frame of the image forming apparatus. In other words, the size of a conventional image forming apparatus cannot be reduced by shortening the conveying path disposed between the photosensitive drum unit 20 and the fixing unit 19.